Security systems such as access control systems are used to control access to buildings and areas within buildings. The magnetic strip found on the back of a work badge may be used for access control. The work badge is scanned across a reader, which reads the information encoded in the magnetic strip, and sends that information to a computer. The computer consults a database to make an access decision. The access decision might be to unlock a door-locking mechanism.
This type of security system, and security systems in general, are not fool proof because security situations are dynamic. Security situations can change at any time granularity, location, or identity. For example, a work badge may be exchanged between individuals. The access control system might be able to authenticate access for a particular work badge, but it might not be able to verify that the work badge is actually possessed by the authorized person.